Coexistence of Cellular and IEEE 802.11 Technologies in Unlicensed Spectrum Bands -A Survey

This paper provides a comprehensive survey on the coexistence of cellular and IEEE 802.11 standards from a holistic viewpoint that takes into account the coexistence of all existing and future cellular and IEEE 802.11 standards in all the available unlicensed spectrum bands. Unlike existing survey works focusing mostly on any unlicensed band and/or standard, we start by giving an overview of unlicensed spectrum bands, including 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. We then review the operation of cellular technologies, namely Long-Term Evolution Unlicensed (LTE-U), Licensed Assisted Access (LAA), and New Radio Unlicensed (NR-U), worldwide in the unlicensed spectrum bands. Further, we summarize scenarios and categories of coexistence mechanisms, conditions for a fair coexistence, and coexistence-related features. An extensive study on the coexistence mechanisms, deployment scenarios, as well as standardization efforts for the coexistence between cellular and IEEE 802.11 standards, is carried out. Finally, we highlight the coexistence challenges and open problems, the convergence of the Third Generation Partnership Project (3GPP) and IEEE standards, as well as future research directions. Moreover, to provide insights on the relative measures, we also carry out comparative studies of several key concerns with regard to the coexistence, namely unlicensed spectrum band, regulatory requirement, coexistence mechanism, and cellular standardization effort. Each study presents a comparison among potential features of one of these concerns in tabular forms. Finally, we summarize key lessons that are learned and discussed throughout the paper.